Perovskite solar cell and preparation method thereof

Abstract

The invention belongs to the technical field of perovskite solar cells, and particularly relates to a perovskite solar cell and a preparation method. The perovskite solar cell comprises a hole transport layer, the hole transport layer is doped with N1, N1, N4, N4-tetra (4-bromophenyl) benzene-1, 4-diamine containing a plurality of aromatic rings to serve as a bridging agent, due to the small molecule flexibility, the hole transport layer can be inserted between 2, 2 ', 7, 7'-tetra [N, N-di (4-methoxyphenyl) amino]-9, 9 '-spirobifluorene molecules, the hole transport path is shortened, and the hole transport efficiency is improved. The transition potential barrier is reduced; and the electron delocalization degree of the bridging agent is relatively high, so that hole transport can be promoted by doping, a carrier transport path is optimized, the conductivity of the material is improved, and the photoelectric conversion efficiency of the device is improved. Components in the hole transport layer are tightly and orderly arranged, so that bidirectional improvement of efficiency and stability is realized.

Description

Technical Field

[0001] This invention belongs to the field of perovskite solar cell technology, and particularly relates to a perovskite solar cell and its preparation method. Background Technology

[0002] Since researchers fabricated the first perovskite solar cell with a photoelectric conversion efficiency of 3.8% in 2009, perovskite solar cells have undergone more than a decade of development, and their efficiency has exceeded 26%, approaching that of commercially available polycrystalline silicon solar cells. Compared to crystalline silicon cells, perovskite solar cells have advantages such as lower production costs and the ability to operate normally in low-light environments such as cloudy or rainy days. Furthermore, perovskite cells can further improve their photoelectric conversion efficiency through stacking. Among various perovskite solar cells, the organic molecule Spiro-OMeTAD (2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene) has become a commonly used hole transport material in perovskite solar cells due to its suitable energy levels and good film-forming properties, achieving high photoelectric conversion efficiency. However, Spiro-OMeTAD also suffers from significant steric hindrance and a high glass transition temperature, leading to relatively disordered intermolecular packing and weak interactions, thus limiting carrier transport to some extent, and there is still room for improvement in device performance. Furthermore, as battery efficiency continues to improve due to the increasing crystallinity of the perovskite layer and electron transport layer, the amorphous morphology of the hole transport layer is becoming increasingly disadvantageous. The electrical conductivity of the hole transport layer remains crucial for improving photoelectric conversion efficiency.

[0003] Improving internal binding strength to enhance order is an effective strategy for improving electrical conductivity. Previous work has prepared single-crystal Spiro-OMeTAD hole transport layers, increasing hole mobility by three orders of magnitude, revealing the importance of mesoscale molecular order for material conductivity. Others have obtained undoped polycrystalline Spiro-OMeTAD, effectively improving the conductivity of undoped materials while enhancing molecular packing. These studies demonstrate that strengthening the internal binding strength of the hole transport layer contributes to improved charge transport. π-π packing is a crucial way to enhance intermolecular bonding. Some studies have doped the hole transport layer with additives containing specific functional groups, such as ethylene glycol side chains, which induce Spiro-OMeTAD recombination through hydrogen bonding, enhancing packing and improving component arrangement order, further improving charge transport. Previous researchers have also doped Spiro-OMeTAD with long-chain polymers containing thiophene fused ring units, improving molecular packing order by anchoring Spiro-OMeTAD with aromatic rings, thus enhancing charge transport performance. These improved thin-film deposition methods or the design of new dopants with specific functional groups to enhance the conductivity of hole transport materials demonstrate the importance of improving the internal order of arrangement. However, there are two limitations: first, the crystalline Spiro-OMeTAD obtained by the former method is constrained by problems such as interface lattice mismatch, and cannot significantly improve device efficiency; second, the design and synthesis of new molecules under the latter approach is both time-consuming and the results are difficult to determine. Therefore, currently, there is a lack of simple and effective solutions for enhancing the conductivity of Spiro-OMeTAD, the core component of charge transport in hole transport layers, through targeted regulation. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, this invention provides a perovskite solar cell and its preparation method. By doping with small molecule bridging agents with multiple aromatic rings and high self-electron delocalization, the internal binding strength of the hole transport layer can be enhanced, thereby optimizing the carrier transport path and achieving high conductivity and high stability.

[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0006] On one hand, this application provides a perovskite solar cell comprising a hole transport layer, the hole transport layer comprising 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, N1,N1,N4,N4-tetrakis(4-bromophenyl)phenyl-1,4-diamine and lithium bis(trifluoromethanesulfonyl)imide.

[0007] Optionally, the hole transport layer is prepared by spin-coating a hole transport layer solution, wherein the solute in the hole transport layer solution includes 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, N1,N1,N4,N4-tetrakis(4-bromophenyl)phenyl-1,4-diamine and lithium bis(trifluoromethanesulfonyl)imide;

[0008] The molar ratio of 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene to N1,N1,N4,N4-tetratetra(4-bromophenyl)phenyl-1,4-diamine is (10~20):1; the molar ratio of lithium bis(trifluoromethanesulfonylimide) to 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene is 1:(1-3).

[0009] Optionally, the spin coating speed for obtaining the hole transport layer solution is 2000-4000 rpm.

[0010] Optionally, the solvent in the hole transport layer solution includes chlorobenzene and 4-tert-butylpyridine.

[0011] Optionally, it includes a transparent conductive substrate and an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and a metal electrode sequentially stacked on the transparent conductive substrate.

[0012] Optionally, the hole transport layer has a thickness of 200nm-400nm; and / or, the electron transport layer has a thickness of 20nm-200nm; the perovskite light-absorbing layer has a thickness of 300nm-700nm; and the metal electrode has a thickness of 80nm-100nm.

[0013] Optionally, the electron transport layer includes one or more of TiO2 and SnO2.

[0014] Optionally, the material of the perovskite transport layer includes ABX3, wherein A is selected from cesium ions, methylammonium ions, or formamidinium ions; and B is selected from Pb. 2+ or Sn 2+ X is selected from I - , Br - or Cl - .

[0015] Optionally, the transparent conductive substrate is a glass substrate with an FTO or ITO conductive film deposited on its surface.

[0016] Optionally, the metal electrode is a gold electrode or a silver electrode.

[0017] On the other hand, this application also provides a method for preparing the perovskite solar cell described in the first aspect, comprising the following steps:

[0018] An electron transport layer is obtained by depositing a TiO2 or SnO2 layer on a transparent conductive substrate;

[0019] A perovskite precursor solution is coated onto an electron transport layer, and then the solvent in the perovskite precursor solution is removed by evaporation and annealing to obtain a perovskite light-absorbing layer.

[0020] A hole transport layer solution was spin-coated onto the surface of a perovskite light-absorbing layer to obtain a hole transport layer; the solutes in the hole transport layer solution included 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, N1,N1,N4,N4-tetrakis(4-bromophenyl)phenyl-1,4-diamine and lithium bis(trifluoromethanesulfonyl)imide;

[0021] Perovskite solar cells are fabricated by depositing electrodes on the hole transport layer.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] This invention utilizes N1,N1,N4,N4-tetra(4-bromophenyl)phenyl-1,4-diamine, containing multiple aromatic rings, as a bridging agent. Due to its small molecule flexibility, it can insert between Spiro-OMeTAD molecules, shortening the hole transport path, lowering the transition barrier, and thus promoting hole transport and optimizing the carrier transport path. Simultaneously, because the selected bridging agent molecule has electron-withdrawing substituents on its outer surface and a conjugated structure internally, it forms a "push-pull structure" for electrons. The high degree of electron delocalization within the bridging agent molecule ensures good electrical conductivity. Therefore, this doping improves the conductivity of the material, thereby increasing the photoelectric conversion efficiency of the device.

[0024] The components inside the hole transport layer are arranged in a close and orderly manner, which helps to reduce the erosion of the perovskite layer by moisture, oxygen and other substances, and is conducive to improving the stability of the battery, thereby achieving a dual improvement in efficiency and stability. Attached Figure Description

[0025] Figure 1 The test results show the GIWAXS characterization of the hole transport layer;

[0026] Figure 2 The results are the test results of SCLC characterization of perovskite solar cells;

[0027] Figure 3 A comparison of the efficiency of perovskite solar cells;

[0028] Figure 4 The comparison shows the hydrophobic angles of the hole transport layer, where a is Comparative Example 1 and b is Example 1.

[0029] Figure 5 The results are the battery fill factor and open circuit voltage test results, where a is the fill factor and b is the open circuit voltage.

[0030] Figure 6 This is a schematic diagram of the perovskite solar cell structure of the present invention;

[0031] Figure 7 A photograph of the actual manufactured battery;

[0032] Figure 8 This is a comparison of the efficiency of the perovskite solar cells in Comparative Example 2 and Comparative Example 1. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings:

[0034] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0035] This application provides a perovskite solar cell, such as Figure 6 As shown, the device includes a transparent conductive substrate and, sequentially stacked on the transparent conductive substrate, an electron transport layer, a perovskite light-absorbing layer, the hole transport layer, and a metal electrode. The hole transport layer comprises 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, N1,N1,N4,N4-tetrakis(4-bromophenyl)phenyl-1,4-diamine, and lithium bis(trifluoromethanesulfonyl)imide.

[0036] In some embodiments of the present invention, the hole transport layer is prepared by spin-coating a hole transport layer solution, wherein the solute in the hole transport layer solution includes 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, N1,N1,N4,N4-tetrakis(4-bromophenyl)phenyl-1,4-diamine and lithium bis(trifluoromethanesulfonylimide);

[0037] The molar ratio of 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene to N1,N1,N4,N4-tetratetra(4-bromophenyl)phenyl-1,4-diamine is (10~20):1; the molar ratio of lithium bis(trifluoromethanesulfonylimide) to 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene is 1:(1-3).

[0038] In some embodiments of the present invention, the spin coating speed for obtaining the hole transport layer solution is 2000-4000 rpm.

[0039] In some embodiments of the present invention, the solvent in the hole transport layer solution includes chlorobenzene and 4-tert-butylpyridine.

[0040] In some embodiments of the present invention, the substrate includes a transparent conductive substrate and an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and a metal electrode sequentially stacked on the transparent conductive substrate.

[0041] In some embodiments of the present invention, the hole transport layer has a thickness of 100nm-400nm; and / or, the electron transport layer has a thickness of 20nm-200nm; the perovskite light-absorbing layer has a thickness of 300nm-700nm; and the metal electrode has a thickness of 80nm-100nm.

[0042] In some embodiments of the present invention, the electron transport layer comprises one or more of TiO2 and SnO2.

[0043] In some embodiments of the present invention, the material of the perovskite transport layer includes ABX3, wherein A is selected from cesium ions, methylammonium ions, or formamidinium ions; and B is selected from Pb. 2+ or Sn 2+ X is selected from I - , Br - or Cl - .

[0044] In some embodiments of the present invention, the transparent conductive substrate is a glass substrate on which an FTO or ITO conductive thin film is deposited.

[0045] This application also provides a method for preparing the above-mentioned perovskite solar cell, comprising the following steps:

[0046] An electron transport layer is obtained by depositing a TiO2 or SnO2 layer on a transparent conductive substrate;

[0047] A perovskite precursor solution is coated onto the electron transport layer, and then the solvent in the perovskite precursor solution is removed by evaporation and annealing to grow a perovskite material layer to obtain a perovskite light-absorbing layer.

[0048] A hole transport layer solution was spin-coated onto the surface of a perovskite light-absorbing layer to obtain a hole transport layer; the solutes in the hole transport layer solution included 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, N1,N1,N4,N4-tetrakis(4-bromophenyl)phenyl-1,4-diamine and lithium bis(trifluoromethanesulfonyl)imide;

[0049] Perovskite solar cells are fabricated by depositing electrodes on the hole transport layer.

[0050] In this application, the transparent conductive substrate is a glass substrate with an FTO or ITO conductive film deposited on its surface. Specifically, an FTO or ITO conductive film can be deposited on the glass substrate to form a transparent conductive substrate, or a commercially available glass substrate covered with FTO or ITO can be used directly. In the embodiments of this application, the commercially available transparent conductive substrate was purchased from Liaoning Youxuan.

[0051] Before fabricating subsequent layers on a transparent conductive substrate, certain positions are typically reserved on both sides of the substrate for later gold electrode deposition as negative electrodes. These negative electrodes generally (do not contact the electron transport layer, perovskite layer, or hole transport layer). This method of reserving gold negative electrode positions can be achieved by applying adhesive tape before fabricating the electron transport layer, then removing the tape during gold electrode fabrication before deposition, or by directly fabricating the electron transport layer, perovskite layer, and hole transport layer sequentially on FTO / ITO, and then scraping off the previously fabricated layers at the desired gold electrode locations with a special tool to expose the underlying FTO / ITO conductive film before electrode deposition. These are conventional techniques in this field and will not be elaborated further. The final fabricated battery is as follows... Figure 7 As shown.

[0052] Example 1

[0053] A perovskite solar cell, the fabrication steps of which are as follows:

[0054] 1. A transparent conductive substrate (2cm*2cm) is subjected to UV ozone treatment for approximately 30 minutes to enhance surface wettability. Then, a dense SnO2 (or TiO2 in other embodiments) layer is deposited as an electron transport layer via spin coating (or screen printing or spray pyrolysis in other embodiments). The spin coating parameters are: 150µL of 3% SnO2 aqueous solution, 3000rpm spin speed, 30s spin coating time, and annealing at 150°C for 30min. The resulting electron transport layer thickness is [not specified]. Due to the aforementioned details regarding the reserved gold negative electrode, the main SnO2 area is approximately 280mm². 2 .

[0055] 2. Treat the material in (I) with ultraviolet ozone for about 30 minutes, and then cover the perovskite precursor solution on the electron transport layer by spin coating (scraping or spraying can also be used in other embodiments). Then remove the solvent in the perovskite precursor solution by evaporation and annealing to obtain the perovskite transport layer. The perovskite precursor solution can be a MAPbI3 solution obtained by dissolving PbI2 and MAI (CH3NH3I) solutes in DMF (N,N-dimethylformamide) and DMSO (dimethyl sulfoxide), or a FAPbI3 solution obtained by dissolving PbI2, MACl (CH3NH3Cl), and FAI (CH5IN2) solutes in DMF and DMSO. When spin-coating the perovskite precursor solution, if the perovskite precursor solution is a MAPbI3 solution, the spin-coating speed is 4000 rpm, the spin-coating time is 25 s, and 500 μL of the antisolvent chlorobenzene is continuously added dropwise for 3-4 s after the 5th s after the start of spin-coating. The annealing condition is 100℃. Annealing for 10 min; the perovskite precursor solution in this example was an FAPbI3 solution (where the solvents were DMF and DMSO, with amounts of 750 μL and 250 μL respectively, used to dissolve 0.8805 g of PbI2, 0.3095 g of FAI, and 0.04254 g of MACl solute). During spin coating, the spin coating volume was 70 μL, the spin speed was 5000 rpm, the spin coating time was 30 s, and 750 μL of the antisolvent diethyl ether was continuously added dropwise for about 2 s after the start of spin coating. The annealing conditions were annealing at 150 °C for 20 min. The resulting perovskite transport layer mainly had an area of ​​approximately 280 mm². 2 .

[0056] III. A hole transport layer solution is spin-coated onto the perovskite light-absorbing layer in (II) to prepare a hole transport layer with a main coverage area of ​​approximately 280 mm². 2 ;

[0057] In this embodiment, the hole transport layer solution includes: solvent chlorobenzene and tributyl phosphate (tBP); the solutes are 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene (Spiro-OMeTAD), N1,N1,N4,N4-tetratetra(4-bromophenyl)phenyl-1,4-diamine, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), wherein the molar ratio of Spiro-OMeTAD to the bridging agent N1,N1,N4,N4-tetratetra(4-bromophenyl)phenyl-1,4-diamine is 18:1, and the molar ratio of chlorobenzene to tBP to LiTFSI to Spiro-OMeTAD is approximately 117.7 : 6.47 : 1 : 1.8.

[0058] The solute and solvent are mixed and stirred at 20℃-30℃ for 6-24 hours. After standing until thermodynamically stable, a hole transport layer solution is obtained. Then, 70 μL of the hole transport layer solution is spin-coated onto the perovskite light-absorbing layer at a spin speed of 3000 rpm for 30 s to obtain the hole transport layer.

[0059] The LiTFSI solute is dissolved in acetonitrile solvent (the amount of acetonitrile is very small, just enough to dissolve LiTFSI), and then added in the required amount to facilitate its uniform dispersion in the Spiro-OMeTAD chlorobenzene solution.

[0060] IV. A 100nm thick Au metal electrode (Ag electrode can also be used) is deposited on the hole transport layer in (III) to obtain a perovskite solar cell.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that the hole transport layer does not include N1,N1,N4,N4-tetra(4-bromophenyl)phenyl-1,4-diamine.

[0063] Comparative Example 2

[0064] The difference between this embodiment and Example 1 is that N1,N1,N4,N4-tetraphenyl-1,4-diamine was replaced with N1,N1,N4,N4-tetra(4-bromophenyl)phenyl-1,4-diamine, with the same molecular weight, in the hole transport layer. However, no improvement in photoelectric conversion efficiency was obtained. (See...) Figure 8 .

[0065] Performance testing:

[0066] Figure 1 The test results of GIWAXS characterization of the hole transport layer are presented. Compared with Comparative Example 1, the π-π stacking distance of the hole transport layer film in Example 1 is shortened, indicating that the intermolecular stacking is more compact and ordered.

[0067] Figure 2 The test results of the SCLC method characterization of the perovskite solar cell show that, based on the slope, the hole transport layer in Example 1 has fewer defects compared to Comparative Example 1, indicating that carrier recombination is suppressed.

[0068] Figure 3 The statistical results of the efficiency of the perovskite solar cells show that, compared with Comparative Example 1, the cell of Example 1 has a higher photoelectric conversion efficiency.

[0069] Furthermore, the close arrangement of components within the hole transport layer helps reduce the erosion of the perovskite layer by moisture, oxygen, and other substances, thus contributing to improved stability. Figure 4 As shown, in Example 1, the hole transport layer modified with N1,N1,N4,N4-tetra(4-bromophenyl)benzene-1,4-diamine has an increased hydrophobic angle, which helps to block water vapor and other substances from eroding the perovskite layer, thereby helping to improve stability.

[0070] like Figure 5 As shown, compared to Comparative Example 1, the fill factor and open-circuit voltage of the cell in Example 1 are improved, which is attributed to improvements in carrier bulk transport and interface extraction. This will provide new ideas and methods for promoting the further industrial production and commercial application of perovskite solar cells.

[0071] This invention adds a bridging agent to the hole transport layer of Spiro-OMeTAD. Due to the multi-aromatic ring characteristic of the bridging agent, it can tightly bind with Spiro-OMeTAD molecules through π-π stacking. Simultaneously, the flexibility of the small molecule allows the bridging agent to insert between Spiro-OMeTAD molecules, shortening the hole transport distance, reducing the transition barrier, thereby optimizing the carrier transport path and improving conductivity. Furthermore, the tight arrangement of the hole transport layer components also prevents moisture and other substances from eroding the perovskite layer, improving device stability.

Claims

1. A perovskite solar cell, characterized in that, It includes a hole transport layer comprising 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, N1,N1,N4,N4-tetrakis(4-bromophenyl)phenyl-1,4-diamine and lithium bis(trifluoromethanesulfonyl)imide.

2. The perovskite solar cell according to claim 1, characterized in that, The hole transport layer is prepared by spin-coating a hole transport layer solution, wherein the solutes in the hole transport layer solution include 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, N1,N1,N4,N4-tetrakis(4-bromophenyl)phenyl-1,4-diamine and lithium bis(trifluoromethanesulfonylimide); The molar ratio of 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene to N1,N1,N4,N4-tetratetra(4-bromophenyl)phenyl-1,4-diamine is (10~20):1; the molar ratio of lithium bis(trifluoromethanesulfonylimide) to 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene is 1:(1-3).

3. The perovskite solar cell according to claim 1, characterized in that, The hole transport layer solution is spin-coated to obtain the hole transport layer at a spin-coating speed of 2000-4000 rpm.

4. The perovskite solar cell according to claim 2, characterized in that, The solvent in the hole transport layer solution includes chlorobenzene and 4-tert-butylpyridine.

5. The perovskite solar cell according to claim 1, characterized in that, It includes a transparent conductive substrate and an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and a metal electrode, which are sequentially stacked on the transparent conductive substrate.

6. The perovskite solar cell according to claim 5, characterized in that, The hole transport layer has a thickness of 200nm-400nm; and / or, the electron transport layer has a thickness of 20nm-200nm; the perovskite light-absorbing layer has a thickness of 300nm-700nm; and the metal electrode has a thickness of 80nm-100nm.

7. The perovskite solar cell according to claim 5, characterized in that, The electron transport layer includes one or more of TiO2 and SnO2.

8. The perovskite solar cell according to claim 5, characterized in that, The perovskite transport layer is made of ABX3, wherein A is selected from cesium ions, methylammonium ions, or formamidinium ions; and B is selected from Pb. 2+ or Sn 2+ X is selected from I - , Br - or Cl - .

9. The perovskite solar cell according to claim 5, characterized in that, The transparent conductive substrate is a glass substrate with an FTO or ITO conductive thin film deposited on its surface.

10. A method for preparing a perovskite solar cell according to any one of claims 1-9, characterized in that, Includes the following steps: An electron transport layer is obtained by depositing a TiO2 or SnO2 layer on a transparent conductive substrate; A perovskite precursor solution is coated onto the electron transport layer, and then the solvent in the perovskite precursor solution is removed by evaporation and annealing to obtain a perovskite light-absorbing layer. A hole transport layer solution was spin-coated onto the surface of a perovskite light-absorbing layer to obtain a hole transport layer; the solutes in the hole transport layer solution included 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, N1,N1,N4,N4-tetrakis(4-bromophenyl)phenyl-1,4-diamine and lithium bis(trifluoromethanesulfonyl)imide; Electrodes are deposited on the hole transport layer to prepare perovskite solar cells.

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